Electrical insulation coating saturated with magnesium and/or calcium ions

ABSTRACT

A composition for providing an electrically insulative coating on electrical alloys having a high permeability and a low core loss which consists essentially of an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from at least one metal in Group II A of the periodic table, which are at least in part provided as the oxide, hydroxide, carbonate, bicarbonate and/or chromate of the Group II A metal or metals. A method for providing an electrically insulative coating on an electrical alloy having a high permeability and a low core loss comprising the steps of coating the alloy with the composition of this invention and curing the coating. A composite article comprising at least one layer of an electrical alloy having a high permeability and a low core loss and at least one layer of a substantially water insoluble, electrically insulative coating which is comprised of a saturated level of Group II A metal cations and anionic polymeric chains of chromium, oxygen and phosphorus atoms.

United States Patent Miller, Jr.

1451 Apr. 25, 1972 [72] Inventor:

[73] Assignee:

Clarence L. Miller, Jr., Pittsburgh, Pa.

Allegheny Ludlum Steel Corporation, Pittsburgh, Pa.

[22] Filed: Jan. 2, 1970 [21] Appl.N0.: 436

[52] U.S. Cl ..117/230, 117/128, 117/129, 117/169, 148/616, 148/62, 148/627, 252/632, 252/635 [51] Int. Cl. ..HOlb 3/02 [58] Field of Search ..252/63.5, 63.2; 148/616, 6.2, 148/627; 117/128, 129, 169, 222, 223, 230

[56] References Cited UNlTED STATES PATENTS 2,753,282 7/1956 Perry ..148/6.16 2,669,636 2/1954 Rawles.....

Rairden Vedder ..338/238 3,477,058 ll/l969 Primary Examiner-John T. Goolkasian Assistant Examiner-M. E. McCamish AttorneyRichard A. Speer, Vincent G. Gioia and Howard R. Berkenstock, Jr.

[ ABSTRACT A composition for providing an electrically insulative coating on electrical alloys having a high permeability and a low core loss which consists essentially of an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from at least one metal in Group 11 A of the periodic table, which are at least in part provided as the oxide, hydroxide, carbonate, bicarbonate and/or chromate of the Group II A metal or metals.

A method for providing an electrically insulative coating on an electrical alloy having a high permeability and a low core loss comprising the steps of coating the alloy with the composition of this invention and curing the coating.

A composite article comprising at least one layer of an electrical alloy having a high permeability and a low core loss and at least one layer of a substantially water insoluble, electrically insulative coating which is comprised of a saturated level of Group II A metal cations and anionic polymeric chains of chromium, oxygen and phosphorus atoms.

21 Claims, No Drawings ELECTRICAL INSULATION COATING SATURATED WITH MAGNESIUM AND/OR CALCIUM IONS The present invention relates to an electrically insulative coating solution, to a method for providing an electrically insulative coating on an alloy having a high permeability and a low core loss and to a composite article comprising an alloy having a high permeability and a low core loss and a layer of electrically insulative coating.

The evolvement of electrical alloys having high permeability and low core loss has made the development of more efficient and powerful electrical equipment possible. A large percentage of these alloys contain iron. Included within this group of electrical alloys are silicon-iron alloys (grain oriented and non-oriented), nickel-iron alloys, cobalt-iron alloys, vanadium permendur and supermendur. Silicon-iron alloys are, however, probably the most important electrical alloys and, accordingly, specific reference in the followingdiscussion is directed to them.

The cores of transformers and other electrical equipment are constructed of laminations to restrict the flow of eddy currents, which thereby reduces core losses. Each lamina must, however, be insulated from the others in order to prevent the eddy current from flowing between lamina. Normal surface oxides which appear on fully-annealed silicon-steel sheets supply a certain amount of this insulation. In many instances this insulation must be supplemented. The additional insulation can be provided by coating the silicon-steel with a material which has good electrical resistance and which will withstand normal operating conditions; e.g., temperature and pressure.

Insulating coating solutions formed from primary magnesium phosphate, mono basic ammonium phosphate, chromic acid anhydride and water are described in U.S. Pat. No. 2,753,282. They are comprised of 5 to 75 parts by weight of primary magnesium phosphate, to 135 parts by weight of mono basic ammonium phosphate, and l to 6 parts by weight of chromic acid anhydride per 100 parts by weight of water.

I have discovered that the insulating characteristics of coating solutions which resemble those described in US. Pat. No. 2,753,282 can be materially improved if they are substantially saturated with ions from at least one metal of Group II A of the Periodic Table; e.g., magnesium and/or calcium. I have also found that at least 1 mole percent of the Group II A metal ions should be provided as the oxide, hydroxide, carbonate, bicarbonate and/or chromate of the Group II A metal or metals. Solutions which receive all their Group II A metal ions from the phosphate of the metal or metals have excessive amounts of phosphate ions which could cause them to become hygroscopic and solutions which receive Group II A metal ions from compounds other than the phosphate, oxide, hydroxide, carbonate, bicarbonate and/or chromate have undesirable ions present therein.

It is accordingly an object of this invention to provide an electrically insulative coating solution.

It is another object of this invention to provide a method for providing an electrically insulative coating on an alloy having a high permeability and a low core loss.

It is a further object of this invention to provide a composite article comprising an alloy having a high permeability and a low core loss and a layer of electrically insulative coating.

The composition of the present invention consists essentially of an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group 11 A metal ions from at least one metal in Group 11 A of the periodic table. Calcium and magnesium are the preferred Group II A metal ions as compounds containing calcium and magnesium are readily available. The ions are proportionately present in the aqueous solution as 6 18 mole percent ammonium ions, 21 63 mole percent phosphate ions, 8 24 mole percent chromate ions and 45 mole percent Group II A metal ions from at least one metal in Group II A of the periodic table and preferably as 9 15 mole percent ammonium ions, 30 55 mole percent phosphate ions, 11 mole percent chromate ions and 25 35 mole percent Group II A metal ions from at least one metal in Group II A of the periodic table. In this application, the term phosphate ion includes all ions related to phosphoric acid in an aqueous solution. Thus, the species H PO H PO HPO, and P0 and any polymeric phosphorus oxyacid anions are collectively referred to as phosphate ion. Similarly, CrO in solution may exist as Cr0 Cr O-,, etc., as well as in various protonated forms, all of which are included in the term chromate ion.

The ions; i.e., ammonium, phosphate, chromate and Group II A metal, may be supplied in various ways. Ammonium ions may be supplied as uncombined ammonia, aqueous ammonium hydroxide, or as the phosphate, chromate, carbonate or bicarbonate salts. Phosphate ions are most conveniently supplied as ortho-phosphoric acid. They can also be supplied as magnesium phosphate, ammonium phosphate or magnesium ammonium phosphate. Chromate ions may be supplied as chromium trioxide or as the chromate or dichromate salts of magnesium or ammonium. Group II A metal ions may be su plied as the oxide, hydroxide, carbonate, bicarbonate, phosphate or chromate of the metal or metals. At least 1 mole percent of the Group II A metal ions should, however, be provided as the oxide, hydroxide, carbonate, bicarbonate and/or chromate of the Group II A metal or metals. Solutions which receive all their Group II A metal ions from the phosphate of the metal or metals have excessive amounts of phosphate ions which could cause them to become hygroscopic and solutions which receive Group II A metal ions from compounds other than the phosphate, oxide, hydroxide, carbonate, bicarbonate and/or chromate have undesirable ions present therein;

A wetting agent can be added to the coating solution to insure the best possible wetting action at the metal surface. The use of wetting agents is optional and by no means necessary. A typical wetting agent is Wetanol (Glyco Products, Inc., New York, New York).

The method of this invention comprises the steps of coating an alloy having a high permeability and a low core loss; e.g., silicon-steel, with the aqueous coating solution described above and curing the coating so as to render it substantially water insoluble.

Any of the well known coating methods can be employed. The invention is not dependent upon the use of any particular coating method. Illustrative coating methods are dip coating, flow coating, spray coating, roll coating and spin coating.

Curing is a time and temperature dependent process. Shorter times are required at higher temperatures and longer times are required at lower temperatures. Curing temperatures; i.e., the temperatures at the metallic surfaces, ranging from 400 to 1,900" P have been successfully employed at times ranging from 2 seconds to 4 hours.

The article of this invention is comprised of at least one layer of an alloy having a high permeability and a low core loss; e.g., silicon-steel, and at least one layer of a substantially water insoluble, electrically insulative coating. In a particular embodiment it comprises a plurality ofalloy layers with a layer of coating electrically insulating each alloy layer from adjacent alloy layers. The coating is comprised of a saturated level of Group II A metal cations; e.g., magnesiumcations, and anionic polymeric chains of chromium, oxygen and phosphorous atoms.

The coating should be at least 0.04 mil thick and preferably at least 0.06 mil thick to insure adequate electrical resistance. Material which is stress-relief annealed should have a coating which is less than 0.3 of a mil-thick and preferably less than 0.2 of a mil thick to insure adequate adhesion after stress-relief annealing.

The following examples are illustrative of several aspects of the invention.

EXAMPLE I An aqueous coating solution, hereinafter referred to as solution A," was mixed'from 22.5 g. primary ammonium phosphate, 103.0 g. primary magnesium phosphate, 25 g.

chromic acid and 400 ml. of water. The resultant solution was applied to silicon-steel strip by dipping and metering the solution with grooved rubber rolls. The coating was subsequently cured at 1,200 F for 35 seconds. A cured coating 0.087 mil thick resulted. After curing, the coated silicon-steel was stressrelief annealed in cracked gas at a temperature of l,650 F for 1 hour.

A second aqueous coating solution, hereinafter referred to as solution B," was mixed from 22.5 g. primary ammonium phosphate, 103.0 g. primary magnesium phosphate, 25.0 g. chromic acid and 400 ml. of water. This time 5 g. of magnesium oxide was added to the solution. The resultant solution was applied to silicon-steel strip and cured in a manner similar to that used for applying and curing solution A. A cured coating 0.105 mil thick resulted. After curing, the coated siliconsteel was stress-relief annealed in cracked gas at a temperature of 1,650 F for 1 hour, as was the silicon-steel which was coated with solution A.

The electrical resistance of both silicon-steel strips was evaluated both before and after stress relief annealing using the Franklin value (ASTM Designation A-344-68). A perfect insulator would have a Franklin value of zero (Franklins are reported in amperes) and a perfect conductor would have a Franklin value of l ampere. The Franklin values for solutions A" and B are reported below in Table I.

TABLE 1 Franklin Values Franklin Values Solution (As Coated) (Stress-Relief Annealed) A 0.3 3 0.97 B 0.07 0.48

A study of TAble I reveals that the electrical resistance achieved from coating solution B (lower Franklin values indicate stronger electrical resistance) was far superior to the electrical resistance achieved from coating solution A. This was expected as solution B was saturated with magnesium ions, whereas solution A was not.

Found below in Table II are the mole percentages in which the ammonium ions, phosphate ions, chromate ions and magnesium ions were proportionately present in both solutions A and "B."

Note that solution B had 27.1 mole percent magnesium ion, whereas solution A had 22.8 mole percent magnesium ion. Solution B," therefore, had 4.3 more mole percent magnesium ion than solution A had. This additional magnesium ion was supplied as magnesium oxide. Supplying the additional magnesium ion as magnesium oxide reduced the mole percent of phosphate ion from 55.3 to 52.3. If the additional magnesium ion was supplied by adding additional magnesium phosphate the mole percent of phosphate ion would have been increased from 55.3 to approximately 59.8. Therefore, the suppliance of magnesium ion from magnesium oxide rather than from magnesium phosphate produced a coating solution with 52.3 mole percent phosphate ion rather than 59.8 mole percent phosphate ion.

EXAMPLE 11 Additional silicon-steel samples were coated with coating solution B and cured at l,200 F for seconds. A cured coating 0.1 of a mil thick resulted. After curing, the coated silicon-steel was stress-relief annealed in a variety of gaseous atmospheres at a temperature of 1,550 F for 1 hour.

men-

The electrical resistance of the samples was measured both before and after stress-relief annealing. Found below in Table 111 are the Franklin values.

TABLE 11! Franklin VAlues Franklin Values (Stress-Relief Atmosphere (As Coated) Annealed) Cracked Gas 0.13 0.18 Nitrogen 0.09 0.43 Hydrogen 0.04 0.54 Forming Gas 0.05 0.40 Still Air 0.09 0.02

A study of Table 111 reveals that the coating of this invention is a good insulator both before and after stress-relief annealing and that it stands up extremely well under the reducing effects of hydrogen annealing atmospheres.

It will be apparent to those skilled in the art that the novel principles disclosed herein in connection with specific examples thereof, will suggestvarious other modifications and applications of the same. It is accordingly desired that in c0nstruing the breadth of the appended claims they shall not be limited to the specific examples of the invention disclosed herein.

1 claim:

1. A composition for providing an electrically insulative coating on electrical alloys having a high permeability and a low core loss: which consists essentially of an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from the group consisting of magnesium ions and calcium ions; said ions being proportionately present in said aqueous solution as 6-18 mole percent ammonium ions, 21-63 mole percent phosphate ions, 8-24 mole percent chromate ions and 15-45 mole percent Group 11 A metal ions; at least 1 mole percent of said Group ll A metal ions being provided from a compound of said Group ll A metal from the group consisting of oxides, hydroxides, carbonates, bicarbonates and chromates.

2. A composition according to claim 1 wherein said ions are proportionately present in said aqueous solution as 9-15 mole percent ammonium ions, 30-55 mole percent phosphate ions, 11-20 mole percent chromate ions and 25-35 mole percent Group 11 A metal ions.

3. A composition according to claim 2 wherein said GROUP 11 A metal ions are calcium ions.

4. A composition according to claim 2 wherein said Group I! A metal ions are magnesium ions.

5. A composition according to claim 1 wherein said Group II A metal ions are magnesium ions and wherein said magnesium ions are proportionately present in said aqueous solution as 25 35 mole percent magnesium ions.

6. A method for providing an electrically insulative coating on an electrical alloy having a high permeability and a low core loss, which comprises, the steps of: coating said alloy with an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from the group consisting of magnesium ions and calcium ions and curing said coating so as to render it substantially water insoluble; said ions being proportionately present in said aqueous solution as 6 18 mole percent ammonium ions, 21 -63 mole percent phosphate ions, 8 -24 mole percent chromate ions and 15 -45 mole percent Group II A metal ions; at least 1 mole percent of said Group II A metal ions being provided from a compound of said Group II A metal from the group consisting of oxides, hydroxides, carbonates, bicarbonates and chromates.

7. A method according to claim 6 wherein said electrical alloy contains iron.

8. A method according to claim 7 wherein said ions are proportionately present in said aqueous solution as 9-15 mole percent ammonium ions, 30-55 mole percent phosphate ions, 1l-20 mole percent chromate ions and 25-35 mole percent Group II A metal ions.

9. A method according to claim 7 wherein said Group II A metal ions are calcium ions.

10. A method according to claim 7 wherein said Group II A metal ions are magnesium ions.

11. A method according to claim 10 wherein said magnesium ions are proportionately present in said aqueous solution as 25 35 mole percent magnesium ions.

12. A method according to claim 6 wherein said coating is cured by heating said metallic surface at a temperature of from about 400 F to about 1,900 F for a period of from about 2 seconds to about 4 hours.

13. A method according to claim 6 wherein said electrical alloy is silicon steel.

14. A composite article comprising at least one layer of an electrical alloy having a high permeability and a low core loss and at least one layer of a substantially water insoluble, cured, electrically insulative coating adhered to said electrical alloy; said coating being comprised of a saturated level of Group ll A metal cations from the group consisting of magnesium cations and calcium cations, and anionic polymeric chains of chromium, oxygen and phosphorus atoms; said coating having been formed from an aqueous solution of ammonium ions,

phosphate ions, chromate ions and a substantially saturated level of Group ll A metal ions from the group consisting of magnesium ions and calcium ions, wherein said ions were proportionately present in said aqueous solution as 6 18 mole percent ammonium ions, 21 63 mole percent phosphate ions, 8 24 mole percent chromate ions and 15 45 mole percent Group II A metal ions, and wherein at least 1 mole percent of said Group ll A metal ions were provided from a compound of said Group ll A metal from the group consisting of oxides, hydroxides, carbonates, bicarbonates and chromates.

15. A composite article according to claim 14 wherein said electrical alloy contains iron.

16. A composite article according to claim 15 wherein said Group ll A metal cations are calcium cations.

17. A composite article according to claim 15 wherein said Group II A metal cations are magnesium cations. 1

18. A composite article according to claim 15 wherein said coating is at least about 0.04 mil thick.

19. A composite article according to claim 18 wherein said coating is less than about 0.3 mil thick.

20. A composite article according to claim 15 wherein said Group II A metal cations are magnesium cations and wherein said coating is between about 0.06 and 0.2 mil thick.

21. A composite article according to claim 15 having a plurality of alloy layers with a layer of coating electrically insulating each alloy layer from adjacent alloy layers. 

2. A composition according to claim 1 wherein said ions are proportionately present in said aqueous solution as 9-15 mole percent ammonium ions, 30-55 mole percent phosphate ions, 11-20 mole percent chromate ions and 25-35 mole percent Group II A metal ions.
 3. A composition according to claim 2 wherein said GROUP II A metal ions are calcium ions.
 4. A composition according to claim 2 wherein said Group II A metal ions are magnesium ions.
 5. A composition according to claim 1 wherein said Group II A metal ions are magnesium ions and wherein said magnesium ions are proportionately present in said aqueous solution as 25 - 35 mole percent magnesium ions.
 6. A method for providing an electrically insulative coating on an electrical alloy having a high permeability and a low core loss, which comprises, the steps of: coating said alloy with an aqueous solution containing ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from the group consisting of magnesium ions and calcium ions and curing said coating so as to render it substantially water insoluble; said ions being proportionately present in said aqueous solution as 6 - 18 mole percent ammonium ions, 21 -63 mole percent phosphate ions, 8 -24 mole percent chromate ions and 15 -45 mole percent Group II A metal ions; at least 1 mole percent of said Group II A metal ions being provided from a compound of said Group II A metal from the group consisting of oxides, hydroxides, carbonates, bicarbonates and chromates.
 7. A method according to claim 6 wherein said electrical alloy contains iron.
 8. A method according to claim 7 wherein said ions are proportionately present in said aqueous solution as 9-15 mole percent ammonium ions, 30-55 mole percent phosphate ions, 11-20 mole percent chromate ions and 25-35 mole percent Group II A metal ions.
 9. A method according to claim 7 wherein said Group II A metal ions are calcium ions.
 10. A method according to claim 7 wherein said Group II A metal ions are magnesium ions.
 11. A method according to claim 10 wherein said magnesium ions are proportionately present in said aqueous solution as 25 - 35 mole percent magnesium ions.
 12. A method according to claim 6 wherein said coating is cured by heating said metallic surface at a temperature of from about 400* F to about 1,900* F for a period of from about 2 seconds to about 4 hours.
 13. A method according to claim 6 wherein said electrical alloy is silicon steel.
 14. A composite article comprising at least one layer of an electrical alloy having a high permeability and a low core loss and at least one layer of a substantially water insoluble, cured, electrically insulative coating adhered to said electrical alloy; said coating being comprised of a saturated level of Group II A metal cations from the group consisting of magnesium cations and calcium cations, and anionic polymeric chains of chromium, oxygen and phosphorus atoms; said coating having been formed from an aqueous solution of ammonium ions, phosphate ions, chromate ions and a substantially saturated level of Group II A metal ions from the group consisting of magnesium ions and calcium ions, wherein said ions were proportionately present in said aqueous solution as 6 - 18 mole percent ammonium ions, 21 - 63 mole percent phosphate ions, 8 - 24 mole percent chromate ions and 15 - 45 mole perCent Group II A metal ions, and wherein at least 1 mole percent of said Group II A metal ions were provided from a compound of said Group II A metal from the group consisting of oxides, hydroxides, carbonates, bicarbonates and chromates.
 15. A composite article according to claim 14 wherein said electrical alloy contains iron.
 16. A composite article according to claim 15 wherein said Group II A metal cations are calcium cations.
 17. A composite article according to claim 15 wherein said Group II A metal cations are magnesium cations.
 18. A composite article according to claim 15 wherein said coating is at least about 0.04 mil thick.
 19. A composite article according to claim 18 wherein said coating is less than about 0.3 mil thick.
 20. A composite article according to claim 15 wherein said Group II A metal cations are magnesium cations and wherein said coating is between about 0.06 and 0.2 mil thick.
 21. A composite article according to claim 15 having a plurality of alloy layers with a layer of coating electrically insulating each alloy layer from adjacent alloy layers. 